Physiologic Response to Microgravity

Physiology in microgravity is a challenging field of research because of limited resources. Though humans have been in space for 50 years most meaningful data has been collected only within the last 15 years. While expensive studies with small sample sizes make obtaining and interpreting data difficult, some general conclusions about the human physiological response to microgravity can be drawn. A redistribution of bodily fluids is believed to initiate change in cardiovascular and respiratory function. The mechanisms for these changes have been studied very little are not well understood. Long term effects of microgravity on the body have been impossible to study in the past. Larger studies must be done for increased time periods in order to better characterize the underlying physiological mechanisms involved in the body’s response to microgravity

Protecting Respiration During Conscious Sedation Using Inspired Carbon Dioxide: A Simulation Study

Conscious sedation procedures require sedation and analgesia sufficient for the particular procedure but not so deep as to cause apnea. Fast acting sedatives such as Propofol are increasingly used in these procedures although they cause more severe respiratory depression than more traditional sedatives such as Midazolam. A method was devised to maintain respiration during conscious sedation by administering inspired CO2 as a respiratory stimulant to offset the reduced respiratory drive caused by Propofol. A computer model was implemented which predicts respiratory depression caused by Propofol administration. Simulations of common dosing regimens were performed with and without inspired CO2. For all dosing regimens, adding inspired CO2 prevented the respiration from falling as much as the control and respiration returned to baseline within 4 to 6 minutes. Administering inspired CO2 during conscious sedation seems to be an effective way to prevent respiratory depression according to the best available numerical model

Validation of Novel Indirect Calorimetry System Based on Luminescence Quenching On-Airway Oxygen Sensor

Metabolic gas exchange monitors are frequently used in the intensive care unit to study the oxygen kinetics and appraise the nutritional requirements for acutely ill patients. In a method known as indirect calorimetry, energy expenditure information is obtained non-invasively by measuring the respiratory gases under resting conditions.1-3 A modified Weir equation relates the oxygen consumption (VO2) and the carbon dioxide production (VCO2) to the caloric burn rate.4 The resting energy expenditure (REE) represents approximately 70% of the total energy expenditure (TEE). Critical illness has been shown to alter metabolic rate and influence VO2. Inflammation, sepsis, seizures, and weaning from ventilation increase the VO2, while sedation, muscle paralysis, shock, and hypothermia decrease the VO2. Since underfeeding a patient may increase catabolism and overfeeding is associated with hyperglycemia, increased ventilation requirements, and lipogenesis, it is imperative for the patient’s recovery that the diet meets nutritional requirements

A Model for Anesthetic Washout During Recovery in the Post Anesthesia Care Unit

Hypercapnia with hyperventilation during emergence from anesthesia has been shown to reduce emergence time, yet little is known about how the subsequent recovery in the post anesthesia care unit (PACU) is affected. A mathematical model has been developed to investigate how inhaled anesthetic agents wash out of patients during recovery in order to demonstrate any difference that hypercapnia and hyperventilation during emergence might have on recovery

Sleep Apnea and the Electrode Conundrum

Sleep disorders deprive a large number of people every year of the rest their bodies need. Current sleep diagnostics methods can be expensive and laden with electrodes, wires, and sensors. The distraction of these monitors and electrodes may have a detrimental effect on obtaining true natural state data. The minimization of invasiveness to the patient, and increased in home use will allow a greater number of individuals to properly diagnose their sleeping disorders. A sensorized blanket is proposed as a means to this end

The Evaluation of a Pulmonary Graphical Display in the Medical Intensive Care Unit: A Feasibility Study

How a new graphical monitor such as the pulmonary display will be integrated and accepted by the users is an important step when introducing new information and technology in the ICU. We developed a pulmonary display that depicts pulmonary information for an intubated, mechanically ventilated patient. This study observed caregivers attending ICU patients in the presence of the pulmonary display. Attendings observed the pulmonary display an average of 3 times per visit whereas nurses glanced at it at least once per visit. The pulmonary display showed distinct patterns demonstrating the changing underlying pulmonary physiology. Based on analysis of questionnaires, the pulmonary display was perceived as useful information, a desirable addition to the current ICU monitors, and an accurate representation of patient pulmonary information

Selection of Patient Specific Dosing Schemes for Procedures of Short Duration and Moderate Stimulation Utilizing Multiobjective Optimization Techniques

Modern anesthesia practice uses a combination of drugs to manage pain and sedation. There are often adverse or negative side effects that arise due to the same combination. A control system will be designed that optimizes the delivery of intravenous sedatives and analgesics to allow esophageal instrumentation while minimizing respiratory compromise and loss of responsiveness in spontaneously breathing patients. A cost functional will be developed to combine the multiple optimization goals into a single objective optimization problem. It is not possible to simultaneously optimize all criteria. A compromise solution must be selected. After selecting weighting coefficients, simulations were run and evaluated by the optimization function. The top five were plotted. The peaks for the five selected doses look reasonable. The maintenance infusions are probably too low for someone to tolerate a placed probe. Additional work is needed to investigate this. These results show promise for the development of a multiobjective optimization approach to patient-specific selection of dosing schemes

Minimizing Post-Surgery Time While Providing Adequate Analgesia

Intro-Differences in anesthetic technique when using propofol, remifentanil and fentanyl can result in different emergence and nociception outcomes. After surgery, a brief emergence period combined with an extended duration of analgesia is desired. We propose to use pharmacokinetic (PK)1-4 and pharmacodynamic (PD)5,6 models to find optimized ratios of propofol and remifentanil to shorten emergence time and extend the time until inadequate analgesia is experienced during patient recovery. Modeling has been used to find the optimum effect site concentrations (CeS) for rapid wake up7; however, an optimization technique which also accounts for analgesic effect is desirable. Method-Anesthesiologists gave general anesthesia to 21 patients for laproscopic procedures using propofol, remifentanil, and fentanyl using a standard of care anesthetic technique. Baseline model predictions for CeS were calculated for remifentanil, fentanyl, and propofol. PD response surface models were used to calculate the probabilities of unconsciousness and response to noxious stimulus (30 PSI tibial pressure algometry, a surrogate of postoperative pain) during and after the anesthetic. Post-hoc optimized PK and PD model predictions were made for both sedation and analgesia by varying the ratio of propofol and remifentanil CeS, constrained to the same or higher PD model predicted probabilities, and leaving fentanyl CeS unchanged from baseline. For each patient, optimized changes to the recorded propofol and remifentanil infusions were made every 5 minutes during the general anesthetic. The theoretical improvement provided by the optimization was measured by comparing the time differences between the baseline model predications and the optimized prediction of the emergence time and time to inadequate analgesia. Results-The baseline model predictions found an average emergence time of 8.2 +/- 5.6 minutes after end of surgery and a duration of analgesia of 9.9 +/- 13.6 minutes after patient emergence. The optimized remifentanil and propofol CeS theoretically reduced the emergence time to 3.9 +/- 1.6 (p\u3c0.01, t-test) minutes and increased the duration of adequate analgesia to 15.4 +/- 12.5 (p\u3c0.05, t-test) minutes. Discussion-Optimized ratios of propofol and remifentanil resulted in a theoretically shorter emergence time and a longer period of adequate postoperative analgesia. These results require clinical verification in a new study, but the optimization algorithm shows potential for real-time clinical guidance in drug management

Electric Blower Based Portable Emergency Ventilator

During CPR the victim will most likely be ventilated by a bag-valve-mask. We propose to replace the traditional bag-valvemask with an electric blower ventilator. This handheld feedback controlled device will automatically compensate for mask leak and enable the rescuer to deliver computer controlled respiratory rates and tidal volumes. We will build a working prototype and conduct bench testing to verify that the blower delivers the desired tidal volumes, even with constantly changing leak conditions that exist when a mask that is poorly fit to a victim’s face. In a volunteer study we will observe how typical rescuers use the blower ventilator so we can develop a product that can be easily and correctly used by naïve rescuers. We will conduct human trials in the operating room to demonstrate the safety and efficacy of the blower ventilator